1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy. More particularly, the present invention relates to an electrode assembly in which the cell stack is not contained within a polymeric enclosure separate from the separators enveloping the anode and cathode electrodes. Eliminating a portion of the conventional polymeric enclosure means that more active materials can be provided inside a casing of a specific volume. This, in turn, means that a cell of increased volumetric efficiency can be contained in a particular casing volume.
2. Prior Art
Conventional electrochemical cells are manufactured of a couple comprised of an anode active material and a cathode active material. An example of this is the lithium/silver vanadium oxide (Li/SVO) cell typically used to power implantable medical devices such as cardiac defibrillators, and the like. These electrochemical couples are built with the anode and cathode electrodes housed in their own separator bags or envelopes. Dedicated separators provide redundancy protection from short circuit contact between the electrodes should one of the separator bags tear or become mechanically compromised.
The individual electrodes are then provided in an electrode assembly such as of a jellyroll type of a serpentine anode with interleaved cathode plates as described in U.S. Pat. No. 4,964,877 to Keister et al. This patent is assigned to the assignee of the present invention and incorporated herein by reference. Before the electrode assembly is housed inside a casing, however, it is inserted into a polymeric “bags”, such as of thermoformed ethylene tetra-fluoroethylene (ETFE). The insulator bag provides for electrical insulation between the edges of the electrode assembly and the casing side walls. In a typical Li/SVO cell, the casing serves as the negative terminal connected to the lithium anode while the insulated terminal pin is the positive terminal connected to the cathode electrode. Since the lithium electrode is electrically connected to the casing, it does not need to be isolated or protected from contact with the casing. Thus, an electrically insulative barrier between the anode electrode and the case is not necessary.
The cathode electrode, on the other hand, being electrically connected to the terminal pin is insulated from the casing. Protecting those portions of the cathode electrode not directly opposite the anode electrode from contact with the casing is important to prevent a short circuit condition.